Class

• <DRM Base Positional Light>

Superclass

• <DRM Light Source>

Subclass

• <DRM Positional Light>
• <DRM Spot Light>

Definition

An instance of a concrete class derived from this DRM class is a <DRM Light Source> that radiates in all directions from a specified point in 3D space with a sphere of influence centred at that point, the radius of which is specified by the value of the radius field.

Only objects that are within the sphere of influence of a <DRM Base Positional Light> instance (that is, an instance of one of its concrete subclasses) can be affected by that <DRM Base Positional Light>. Specific subclasses may further restrict the zone of influence to only a portion of the sphere.

The degree to which an object is affected in the zone of influence depends on the attenuation of the <DRM Base Positional Light>, which depends on the values of its attenuation factor fields. If attenuation is not specified - that is, when constant_attenuation_factor = 1,0, linear_attenuation_factor = 0,0, and quadratic_attenuation_factor = 0,0 - the light ends abruptly at the edge of the sphere of influence. Otherwise, the light intensity components (ambient, diffuse, and specular) are attenuated by the reciprocal of the attenuation quadratic (a + bd + cd²), where a, b, c are the attenuation factor field values as noted in their footnotes, and d is the distance from the position of the <DRM Base Positional Light>.

Consequently, the formula for the final attenuation factor is:

                                       1
       --------------------------------------------------------------
       [ constant_attenuation_factor +
            (distance × linear_attenuation_factor) +
                ((distance squared) × quadratic_attenuation_factor) ]

The radius field, which is specified in metres, together with the <DRM Location 3D> component specifies the zone of influence of the given <DRM Base Positional Light> instance.

The constant_attenuation_factor field is the constant “a” in the attenuation quadratic (a + bd + cd²).

The linear_attenuation_factor field is the constant “b” in the attenuation quadratic (a + bd + cd²).

The quadratic_attenuation_factor field is the constant “c” in the attenuation quadratic (a + bd + cd²).

Class diagram

Figure 6.18 — DRM_Base_Positional_Light

Constraints

• Publishable Object

Example(s)

See subclasses for examples.